This invention relates primarily to the sterilizing of medical items such as instruments and linens utilized in hospital's or doctor's offices. The invention is more particularly directed to an article of manufacture that can serve as an indicating device that will provide a positive indication that a proper sterilizing cycle has been provided by an autoclave. The device is also useful as a mechanical actuator responsive to a sterilizing cycle.
U.S. Pat. Nos. 4,247,517, 4,251,482, 4,374,570 and 4,372,921 disclose systems for storing medical items while they are being sterilized, stored, used, and awaiting resterilization. These systems utilize a container that is automatically closed within an autoclave near the completion of a sterilizing cycle so that the articles being sterilized are sealed within a vacuumized container when the container is removed from the autoclave, thus guaranteeing sterility. The primary means employed to obtain the automatic closing of the container is an expandable chamber which captures a quantity of the sterilizing steam utilizing a temperature responsive valve means. The captured steam later causes the chamber to expand and the expansion force is utilized to close or to permit the container to close. The valve closing the chamber is responsive to the steam temperature. Thus it captures the steam fairly early within a sterilizing cycle. It is important however that the chamber not expand to provide an actuating force until near the end of the sterilizing cycle so that steam remains in contact with the container contents during the entire steam phase of the cycle.
It has been found that some malfunctioning have significant pressure variations during the high pressure steam phase of the sterilizing cycle. These pressure variations can cause the expandable chamber to expand sooner than desired with the result that the container contents would not be in contact with further steam entering the autoclave and therefore may not be adequately sterilized.
The problem has been greatly compounded by the recent introduction of a different form of autoclave cycle. Earlier autoclaves provided only a single high pressure steam phase. While as indicated above, the pressure might vary somewhat during such phases, there was at least only one such phase. Recently however there have been introduced autoclaves that employ at the beginning of the cycle several pulses of high pressure steam followed by a short application of pressure reduction to hasten the removal of air and the steam. These bursts of steam might cause the temperature responsive valve means to close the expandable chamber actuator referred to above to capture a quantity of steam, and with the subsequent reduction of pressure would cause the closed chamber to expand thus providing a premature actuating force which would result in the container being closed before the contents have been subjected to the main application of high pressure steam. Accordingly, a need exists for a means to avoid this problem.
In the operation of an autoclave, a related problem which arises is that of knowing whether the autoclave has properly functioned so that there is an assurance that the articles when removed from the autoclave have been properly sterilized. For example, to provide proper sterilization by steam, it is necessary that steam of a certain temperature, pressure and saturation be applied for a certain period of time. An inadequate temperature will not adequately kill the bacteria. With steam of a pressure below a certain level, it is necessary that the temperature be higher or that the steam be applied for a longer period of time. For example, to put this in extreme, dry heat without steam requires a higher temperature for a longer period of time to provide sterilization than does lower temperature high pressure steam.
The current requirement is that steam at 270.degree. F., 97% saturation and 30 psi be applied for at least three minutes. Chemical indicators are employed to attempt to provide assurance as to the adequacy of the sterilizing cycle. However, most of these indicators are primarily temperature responsive. That is, they will give an indication that the environment within the autoclave reached a certain temperature level. However, they do not give an adequate indication as to the length of time that the sterilizing environment was applied, nor do they give an indication that steam was present. Recently chemical indicators have been developed to indicate a minimum time the temperature was at a set level, but even these indicators can be turned by dry heat, and thus do not indicate that steam was present. These indicators employ a crystal that liquefies at a certain temperature and then travels through a wick to measure time.
In addition to providing steam, some autoclaves are separately heated. Thus, this supplementary heating could cause an indicator to suggest that adequate sterilization was obtained when the steaming capability of the autoclave may have malfunctioned or a burst of steam striking the indicator could affect the indicator.
Accordingly, a need exists for an improved indicator that will reliably tell whether a sterilizing cycle has been adequate. In addition to being reliable, such indicators must also be relatively inexpensive to be practical.